WP_Theme::get_screenshot( string $uri = 'uri' )
Returns the main screenshot file for the theme.
Description
The main screenshot is called screenshot.png. gif and jpg extensions are also allowed.
Screenshots for a theme must be in the stylesheet directory. (In the case of child themes, parent theme screenshots are not inherited.)
Parameters
- $uri
-  (string) (Optional) Type of URL to return, either 'relative' or an absolute URI. Defaults to absolute URI. Default value: 'uri' 
Return
(string|false) Screenshot file. False if the theme does not have a screenshot.
Source
File: wp-includes/class-wp-theme.php
public function get_screenshot( $uri = 'uri' ) {
		$screenshot = $this->cache_get( 'screenshot' );
		if ( $screenshot ) {
			if ( 'relative' === $uri ) {
				return $screenshot;
			}
			return $this->get_stylesheet_directory_uri() . '/' . $screenshot;
		} elseif ( 0 === $screenshot ) {
			return false;
		}
		foreach ( array( 'png', 'gif', 'jpg', 'jpeg', 'webp' ) as $ext ) {
			if ( file_exists( $this->get_stylesheet_directory() . "/screenshot.$ext" ) ) {
				$this->cache_add( 'screenshot', 'screenshot.' . $ext );
				if ( 'relative' === $uri ) {
					return 'screenshot.' . $ext;
				}
				return $this->get_stylesheet_directory_uri() . '/' . 'screenshot.' . $ext;
			}
		}
		$this->cache_add( 'screenshot', 0 );
		return false;
	}  Changelog
| Version | Description | 
|---|---|
| 3.4.0 | Introduced. | 
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Licensed under the GNU GPLv2+ License.
    https://developer.wordpress.org/reference/classes/wp_theme/get_screenshot